Preparation of odorless naphthas using silica gel



PREPARATION OF ODORLESS NAPHTHAS USING SILICA GEL George W. Ayers, Chicago, and Walter J. Sandner, Carpentersville, 111., assignors to The Pure i] Company, Chicago, BL, a corporation of Ohio No Drawing. Application September 22, 1955 Serial No. 536,018

4 Claims. (Cl. 208-307) This invention relates to a method of preparing odorless naphthas and, more particularly, to a method of distilling heavy alkylate fractions whereby the tendency to form odor in the fractions is prevented.

The preparation of naphthas, particularly naphthas from heavy alkylate fractions, which are free of odor after treatment and also remain odor-free during storage over extended periods of time, has been an uncertain and tedious operation. One batch of naphtha may have satisfactory odor characteristics, while another batch, prepared in apparently similar fashion, may be wholly unsuitable as an odorless naphtha. There are many processes disclosed in the prior art which relate to removing odorous materials from hydrocarbons and which may be classified as sweetening processes wherein the various sulfur and oxygen compounds which cause some of the odor are chemically modified, removed or absorbed. The steps of these prior art methods, Whether chemical or physical, when applied to alkylate fractions have been found to be inadequate for the removal of ats Patent vention of odor is, therefore, a different problem from deodorization.

In carrying out the invention, very small amounts of silica gel may be used in either continuous or batch distillation, namely, from about 0.001 to 2.0 weight percent based on the weight of naphtha charged. The distillation must be conducted under reduced pressure. In fact, although it is a more expensive expedient, distillation in the absence of any adsorbent material under a very low pressure of 2 mm. of mercury may constitute "a good method of preventing odor development in naphthas but distillation without an adsorbent at 10 to 15 mm. pressure produces naphthas which are sometimes passable and sometimes not passable as far as odor is concerned. With small amounts of silica gel present, higher pressure can be used, in the order of 75 to 115 mm. of mercury and preferably not more than 200 mm. of mercury for consistent results. The use of steam or other inert atmosphere allows the process to be carried out at a higher total pressure than would be permissible otherwise.

Another object of the invention is to provide a process for preventing the formation of odor in heavy alkylates during distillation.

A further object of this invention is to provide a method of preventing the formation of odor and insuring odor stability in heavy alkylate fractions by distilling in the presence of a small amount of silica gel under reduced pressure.

In order to demonstate the invention, a series of experiments was conducted in which a sample of heavy alkylate produced by the hydrofluoric acid alkylation of isobutane with isobutylene was divided into a plurality of samples. This heavy alkylate exhibited the following odor or the prevention of odor formation during storage. distillation characteristics:

TABLE I Tests on heavy alkylwte Per- Per- Per- API gravity I.B.P. 5% 10% 20% 30% E.P. cent cent cent Odor rec. res. loss 54.0 347 354 356 358 360 363 366 369 374 383 414 466 517 98.0 1.6 0.4 Slight (essentially odorless).

' tion does not relate to the removal of odor from naphthas or heavy alkylates which have already deteriorated to the point of being odorous, but rather is directed to the prevention of odor formation during distillation of naphthas or heavy alkylates which are already essentially odor-free but have a decided tendency to go off-odor during storage. Consequently, those processes in the prior art which are concerned with the treatment of cracked naphthas, or naphthas containing sulfur compounds which are notoriously odorous, have no bearing on this disclosure. It has further been found that steam distillation or distillation in the presence of an inert gas under ordinary reduced pressure does not accomplish the desired result. Also, experiments were conducted wherein counter-current contact and percolation techniques were employed using large amounts of silica gel, and it was found that a completely satisfactory, essentially odor-free naphtha was not obtainable. The prc Example 1.500 cc. of the aforedescribed heavy alkylate was placed in a flask with 7.5 grams of 200- mesh silica gel and the mixture was distilled at 110 to 120 mm. of mercury total pressure using 4.5 lbs. of steam per gallon of total distillate. The product, amounting to 375 cc., had practically no odor whatsoever and was satisfactory for use as odorless mineral spirits.

Example 2.500 cc. of this heavy alkylate was distilled with steam in amounts of approximately 4.5 lbs. of steam per gallon of distillate under 90 to mm. total pressure without silica gel being present. The product obtained represented 75% of the change and exhibited such odor as to make it unsuitable as odorless mineral spirits.

Example 3.500 cc. of this heavy alkylate was distilled in the presence of 1.9 grams of 200-mesh silica gel. This amount of silica gel represented about 0.5 weight percent based on the amount of heavy alkylate. Approximately 4.5 lbs. of steam per gallon of distillate was used at to mm. total pressure. A product amounting to 375 cc. of distillate was obtained which was satisfactory for marketing as odorless mineral spirits. In this case, however, the odor was not quite as satisfactory as that of the sample obtained in Example 1 but the odor of the product was still markedly superior to that obtained when no silica gel was used. In order to further demonstrate the invention, a series of distillations was conducted using different pressures, varying amounts of inert gas and varying amounts of silica gel. The results are shown in Table II.

but unstable and tend to form odorous compounds during storage which consists in distilling said hydrocarbon mixtures in the presence of between about 0.001 to 0.5

TABLE II Distillation of heavy alkylate Maximum Maximum Distillate Run Distillation Material added to overhead bottoms yield No. pressure Inert gas used during distillation charge before temp. temp. (percent of Odor of distillate (mm. Hg.) distillation during during charge) distillation distillation Atm. Steam (8.6 lbs. per gal. dist 222 242 75 (Terpene-like) not passable. 77-80 Steam (2.6 lbs. per gal. dist 160 183 75 Do.

2 Nitrogen 134 150 75 (Almost odorless) passable. 100 .do do 252 273 60 (Slight odor) not passable. 113-l22 Steam (5.8 lbs. per. gal. dist.) Silica gel (0.5%). 169 188 75 (Almost odorless) passable. 104-120 Steam (6.9 lbs. per gal. dist.) Silica gel (20%). 163 179 76 Do. I

Atm Steam lbs. per gal. dist.) lo 216 228 7a (Terpene-hlce odor) not passable.

From the foregoing experiments it is apparent that the invention relates broadly to a process of preparing odorless hydrocarbons or naphthas, particularly heavy alkylate fractions, by distillation or vaporization in the presence of at least about .001 Weight percent of silica gel and separating the product. The process is carried out with or Without an inert diluent, such as steam or nitrogen, which may be present in amounts ranging from about to 200 weight percent based on the amount of hydrocarbon being treated. The preferred pressure range is about 10 to 200 mm. of Hg. Although the invention has been described in connection with naphthas, by which is meant hydrocarbon distillation boiling from about 325 to 425 F. or within the gasoline boiling range, it is applicable to other hydrocarbon mixtures which form odor on storage. Thus various polymerization, isomerization, alkylation and hydrogenation products may be treated in accordance with this invention. The process finds particular application in the treatment of heavy a'lkylates, that is, those boiling in the range of about 340 to 580 F. produced by the catalytic reaction of olefins with parafi'ins, because these types of hydrocarbon mixtures are diflicult to transform into essentially odor-free fractions by distillation.

Although the invention has been demonstrated by reference to various examples, these are only illustrative and the only limitations attaching to the invention appear in the appended claims.

What is claimed is:

1. The method of preparing storage-stable, odor-free naphthas from hydrocarbon mixtures which are odor-free Weight percent of silica gel based on the amount of said hydrocarbon mixture, at a pressure of between about 10 to 200 mm. of mercury and in the presence of about 20 to 200 weight percent based on the amount of said hydrocarbon mixture of an inert, vaporizable diluent whereby the formation of odorless products is prevented and collecting a storage-stable, odor-free hydrocarbon distillate.

2. The method in accordance with claim 1 in which the hydrocarbon mixture comprises a heavy alkylate fraction having a boiling range of about 347 to 517 F.

3. The method in accordance with claim 1 in which the diluent is steam.

4. The method in accordance with claim 1 in which the diluent is nitrogen.

References Cited in the file of this patent UNITED STATES PATENTS 1,735,988 Apgar Nov. 19, 1929 1,886,261 Miller et a1 Nov. 1, 1932 2,463,601 Crawford Mar. 8, 1949 2,468,986 Legatski May 3, 1949 2,764,621 Fulton Sept. 25, 1956 2,768,942 Marple et a1. Oct. 30, 1956 2,851,506 Ayers et a1. Sept 9, 1958 OTHER REFERENCES Some Industrial Uses for Silica Gel, September 1921, The Silica Gel Corporation, Baltimore, Md. (29 pages, page 11 only relied on). 

1. THE METHOD OF PREPARING STORAGE-STABLE, ODOR-FREE NAPHTHAS FROM HYDROCARBON MIXTURES WHICH ARE ODOR-FREE BUT UNSTABLE AND TEND TO FORM ODOROUS COMPOUNDS DURING STORAGE WHICH CONSISTS IN DISTILLING SAID HYDROCARBON MIXTURES IN THE PRESENCE OF BETWEEN ABOUT 0.001 TO 0.5 WEIGHT PERCENT OF SILICA GEL BASED ON THE AMOUNT OF SAID HYDROCARBON MIXTURE, AT A PRESSURE OF BETWEEN ABOUT 10 TO 200 MM. OF MERCURY AND IN THE PRESENCE OF ABOUT 20 TO 200 WEIGHT PERCENT BASED ON THE AMOUNT OF SAID HYDROCARBON MIXTURE OF AN INERT, VAPORIZABLE DILUENT WHEREBY THE FORMATION OF ODORLESS PRODUCTS IS PREVENTED AND COLLECTING A STORAGE-STABLE, ODRO-FREE HYDROCARBON DISTILLATE. 